High-temperature quantum Hall effect in finite gapped HgTe quantum wells

We report on the observation of the quantum Hall effect at high temperatures in HgTe quantum wells with a finite band gap and a thickness below and above the critical thickness dc that separates a conventional semiconductor from a two-dimensional topological insulator. At high carrier concentrations, we observe a quantized Hall conductivity up to 60 K with energy gaps between Landau levels of the order of 25 meV, in good agreement with the Landau level spectrum obtained from k·p calculations. Using the scaling approach for the plateau-plateau transition at ν=2→1, we find the scaling coefficient κ=0.45±0.04 to be consistent with the universality of scaling theory, and we do not find signs of increased electron-phonon interaction to alter the scaling even at these elevated temperatures. Comparing the high-temperature limit of the quantized Hall resistance in HgTe quantum wells with a finite band gap with room-temperature experiment in graphene, we find that the energy gaps at the breakdown of the quantization exceed the thermal energy by the same order of magnitude.